Field of the Invention
The present invention relates to a technology for observing the constituents or the shape of the surface and the inside of an object.
Description of the Related Art
A technology of irradiating a biological body with a laser beam to generate an ultrasonic wave (photoacoustic wave) resulting from laser irradiation inside the biological body, and analyzing the photoacoustic wave to analyze the structure or the state of the surface and the inside of the biological body has been devised (U.S. Pat. No. 5,840,023).
This is also referred to as photoacoustic wave measurement, and since an examination is noninvasively performed, there are movements to divert the photoacoustic wave measurement for medical use in order to perform the examination of the inside of a human body.
Additionally, X-ray mammography for the purpose of the examination and the diagnosis of breast cancer is known, and a manual scanning photoacoustic measurement apparatuses have been developed for the purpose of breast cancer examination (S. A. Ermilov et al., Development of laser optoacoustic and ultrasonic imaging system for breast cancer utilizing handheld array probes, Photons Plus Ultrasound: Imaging and Sensing 2009, Proc. of SPIE, vol. 7177, 2009).
The photoacoustic measurement apparatus can acquire various pieces of information on the inside of an object by the wavelength of light applied to the object (hereinafter, irradiation light). For example, when near-infrared light that has a property of being likely to be absorbed in hemoglobin in blood is used, a blood vessel image can be acquired. Additionally, the oxygen saturation in blood can be measured by performing measurement a plurality of times by using irradiation light with a wavelength that is likely to be absorbed in oxygenated hemoglobin, and irradiation light with a wavelength that is likely to be absorbed in reduced hemoglobin, and comparing a plurality of blood vessel images that are acquired.
In a case where the measurement is performed a plurality of times while changing the wavelength of irradiation light, when the positions of ultrasound probe with respect to a measurement segment are different, the acquired images are displaced, so that the comparison cannot be correctly performed. Accordingly, the positions of the ultrasound probe with respect to an object are desirably the same in all of the measurement.
In the manual scanning photoacoustic measurement apparatus, since an illumination optical system, an irradiation port, and an ultrasound probe are housed in a single probe, the relative positions of the irradiation port and the ultrasound probe are fixed. However, it is difficult to manually reproduce the angle of the probe with respect to the object, pressing force each time the measurement is performed.
Therefore, in a case where a plurality of pieces of photoacoustic data are acquired to be compared, measurement is preferably performed a plurality of times at a time in a state where the probe is pressed against the object and maintains the posture, while changing the wavelength of the irradiation light.
However, a certain amount of time is required to switch the wavelength of the irradiation light. Therefore, the conventional photoacoustic measurement apparatus has a problem that unnecessary irradiation light which is not used in measurement is applied to an object when the wavelengths are switched, so that an unwanted physical burden is imposed on an object.